Most vehicle seats, particularly in passenger vehicles, are generally provided with adjustment mechanisms to allow a seat occupant to position the seat for optimal comfort and convenience. A vehicle seat typically includes a seat back that is mounted with a seat bottom. Many vehicle seats also include a recliner mechanism to adjust the angle of the seat back relative to the seat bottom. Vehicle seats can also include mechanisms that allow movement of the seat forward and backward (fore and aft) relative to the floor of the vehicle. To accomplish this, vehicle seats are mounted on a seat support frame that is mounted on first and second spaced apart track assemblies. Each assembly has an upper track connected to the seat support frame that is slidably mounted on a lower track that is fixed to the vehicle floor with a low-friction member or surface between the tracks. The fore and aft axes correspond to a generally horizontal longitudinal direction relative to the vehicle and generally move the seat closer or father away from the steering wheel and operating pedals of the vehicle. A power seat adjuster can be used to control a motor for operating a mechanism that can move the seat on the tracks. The power seat adjuster can also be operated to adjust the seat in a generally vertical or elevational direction. Generally, power seat adjusters control the elevation of the front and rear portions of the seat bottom separately. Thus, the typical power seat adjuster can be operated to adjust the seat in generally three axes: 1) fore and aft; 2) front elevation; and 3) rear elevation.
It is common for such vehicle seat adjustments to be accomplished by manually or electrically controlled mechanical devices using gears, screws, and bell cranks. The limitations of manually controlled seat adjusters is that there are a finite number of positions or stops along a seat track in which the seat can be positioned. These systems also commonly require an individual to reach down to the side or bottom of a seat to activate the release mechanism for adjustment. With power seat adjusters, a motor generally is used to operate a rack and pinion or gear system to cause movement of the seat. A power seat adjuster system is easier to use and allows for greater distance or position control than with a manual system.
A drive mechanism for operating the fore and aft motion of a power seat adjuster typically includes an electric motor which bi-directionally rotates a pair of drive shafts extending outward from the motor to a gear assembly or box mounted on each upper track. A drive block is fixedly mounted to each lower track and threadingly receives a lead screw or threaded shaft to cause reciprocal horizontal movement of the upper track and the attached seat support frame relative to the lower track that is fixed to the vehicle when the drive motor is activated. Steel gimbal drive blocks are known to be used for maintaining alignment between the shaft and drive block. Steel gimbals are difficult to manufacture because of the metal to metal contact they are prone to chuck and rattle. Chucking is typically considered to be undesirable fore and aft play within the mechanism. Additionally, steel on steel gimbals are difficult to align and thus, are prone to squeal. Thus, it would be advantageous to utilize an improved assembly for seat positioning that has self-aligning characteristics while having a low vibration (low noise) transmissivity.